The present invention relates to a sheet-like object feed unit in a sheet-fed rotary printing press, which prevents a sheet-like object from being fed to a printing unit in an abnormal state.
Conventionally, in a sheet-fed rotary printing press, a sheet fed out from a feed unit is conveyed on a feeder board and feedboard, and is jogged in the circumferential direction by the front lay of a registration unit provided at the distal end of the feedboard. The sheet jogged in the circumferential direction is gripped by the gripper of a swing arm shaft pregripper, and is supplied to the impression cylinder of a printing unit through gripping change from the gripper of the swing arm shaft pregripper to the gripper of the impression cylinder. An improper paper feeding detecting means for detecting that a conveyed sheet moves over the front lay or two sheets are fed in an overlaying state, i.e., abnormal or defective paper feeding, is provided at the distal end of the feedboard. When the improper paper feeding detecting means detects improper paper feeding, impression throw-off is performed, and printing is stopped.
In an improper paper feeding detecting apparatus disclosed in Japanese Patent Laid-Open No. 4-347641, an improper paper feeding detector for detecting whether improper paper feeding has occurred and generating a corresponding signal is provided to a registration unit. If the improper paper feeding detector does not detect improper paper feeding, printing is continued in the impression throw-on state. If the improper paper feeding detector detects improper paper feeding, the printing cylinders of all the printing units are disengaged and the printing operation is stopped. At this time, paper conveyance is stopped by a front lay, and the sheets are left in the registration unit so as not be supplied to the printing units.
In the conventional sheet-fed rotary printing press with the improper paper feeding detecting apparatus described above, even when the improper paper feeding detector detects occurrence of improper paper feeding, sometimes paper conveyance cannot be stopped by the front lay well in time. If the sheet is fed over the front lay, it sometimes undesirably reaches the impression cylinder of a printing unit. In this case, the sheet is gripped by the gripper of the impression cylinder, and is conveyed to the delivery unit through gripping change between the grippers of the respective cylinders. During conveyance, if the improperly fed sheet is bent, it applies an excessive printing pressure to the printing cylinder. In particular, when a plurality of sheets are bent, they apply a large pressure, thus damaging the jacket of the impression cylinder and the blanket of the blanket cylinder.
It is an object of the present invention to provide a sheet-like object feed unit in a sheet-fed rotary printing press, which does not damage the surface of a printing cylinder even if improper paper feeding occurs.
In order to achieve the above object, according to the present invention, there is provided a sheet-like object feed unit in a sheet-fed rotary printing press, comprising a convey unit for conveying a sheet-like object, improper feeding detecting means, disposed on a sheet-like object convey path including the convey unit, for detecting improper feeding of the sheet-like object, a first holding unit disposed downstream of the convey unit in a sheet-like object convey direction and having first holding means for holding the sheet-like object conveyed by the convey unit, a second holding unit disposed downstream of the first holding unit in the sheet-like object convey direction and having second holding means for holding the sheet-like object held by the first holding unit, and first disable means for disabling the second holding means when the improper feeding detecting means detects improper feeding of the sheet-like object.